I keep getting errors where the database disk image is corrupted. The restore function is not working. This happens every other day.

Creating a new db and copying existing files works, but I would like to know what might cause the db to become corrupted.

Thanks for advise.

calibre, version 0.8.56
Corrupted database: The library database at Z:\00. DATA\70. Books\SF - Calibre appears to be corrupted. Do you want calibre to try and rebuild it automatically? The rebuild may not be completely successful.

You are using the Library in an network drive, maybe with more then one computers? Or you are deleting manual data from the Calibre Library directory? Maybe you need to check if metadata.db is locked and if why?
If the metadata.db is corrupt and restore can't help, you can delete the file. With next start of Calibre the file will be generated new from the metadata files in the book directories.